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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Generic approach for synthesizing asymmetric nanoparticles and nanoassemblies

A generic route for synthesis of asymmetric nanostructures. This approach utilizes submicron magnetic particles (Fe.sub.3O.sub.4--SiO.sub.2) as recyclable solid substrates for the assembly of asymmetric nanostructures and purification of the final product. Importantly, an additional SiO.sub.2 layer is employed as a mediation layer to allow for selective modification of target nanoparticles. The partially patched nanoparticles are used as building blocks for different kinds of complex asymmetric nanostructures that cannot be fabricated by conventional approaches. The potential applications such as ultra-sensitive substrates for surface enhanced Raman scattering (SERS) have been included.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Modifying a covarying protein–DNA interaction changes substrate preference of a site-specific endonuclease

Abstract Identifying and validating intermolecular covariation between proteins and their DNA-binding sites can provide insights into mechanisms that regulate selectivity and starting points for engineering new specificity. LAGLIDADG homing endonucleases (meganucleases) can be engineered to bind non-native target sites for gene-editing applications, but not all redesigns successfully reprogram specificity. To gain a global overview of residues that influence meganuclease specificity, we used information theory to identify protein–DNA covariation. Directed evolution experiments of one predicted pair, 227/+3, revealed variants with surprising shifts in I-OnuI substrate preference at the central 4 bases where cleavage occurs. Structural studies showed significant remodeling distant from the covarying position, including restructuring of an inter-hairpin loop, DNA distortions near the scissile phosphates, and new base-specific contacts. Our findings are consistent with a model whereby the functional impacts of covariation can be indirectly propagated to neighboring residues outside of direct contact range, allowing meganucleases to adapt to target site variation and indirectly expand the sequence space accessible for cleavage. We suggest that some engineered meganucleases may have unexpected cleavage profiles that were not rationally incorporated during the design process.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

Antimony segregation in Si layers grown by molecular beam epitaxy on Si wafers with different crystallographic orientations

The segregation of Sb in Si layers grown by molecular beam epitaxy on Si substrates with the (111), (110), and (115) crystallographic orientations is studied; the results obtained for these orientations are compared with those obtained for the most widely used orientation (001). It is found that there is a qualitative similarity between the temperature dependences of the Sb segregation ratio (r) for all studied orientations; in particular, it is possible to separate two characteristic temperature ranges corresponding to the kinetically limited and equilibrium regimes of segregation. However, quantitatively, the values of r for the orientations under study differ significantly from those for the Si(001) case at the same temperatures. For all orientations, narrow temperature ranges within which the values of r vary by nearly five orders of magnitude are revealed for all dependences of r on the growth temperature. This finding allows us to adopt the method of selective doping, which was for the first time suggested by us for structures grown on Si (001) and is based on the controlled use of the segregation effect, to structures grown on Si substrates with an orientation different from (001). Using this method, selectively doped Si:Sb/Si(111) structures are fabricated; in these structures, a variation in the Sb concentration by an order of magnitude occurs at the scale of several nanometers.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Oxide dispersion strengthened 304 L stainless steel produced by ink jetting and laser powder bed fusion

This paper discusses the fundamentals of a novel hybrid method to synthesize oxide dispersion strengthened (ODS) 304 L stainless steel (SS) alloy using a modified laser powder bed fusion (LPBF) machine. Previously, ODS metal matrix composites have been produced by LPBF via ball-milling, which is expensive to scale. Here, we selectively dope yttria nanoparticles into a SS matrix by jetting a precursor chemistry onto the SS substrate prior to laser conversion and consolidation. Here, the new alloy shows good room temperature mechanical properties. Microstructures are studied using electron microscopy, energy dispersive spectroscopy and electron backscatter diffraction.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Exploring the Role of the Central Carbide of the Nitrogenase Active-Site FeMo-cofactor through Targeted 13 C Labeling and ENDOR Spectroscopy

Mo-dependent nitrogenase is a major contributor to global biological N 2 reduction, which sustains life on Earth. Its multi-metallic active-site FeMo-cofactor (Fe 7 MoS 9 C-homocitrate) contains a carbide (C 4– ) centered within a trigonal prismatic CFe 6 core resembling the structural motif of the iron carbide, cementite. The role of the carbide in FeMo-cofactor binding and activation of substrates and inhibitors is unknown. Here, to explore this role, the carbide has been in effect selectively enriched with 13 C, which enables its detailed examination by ENDOR/ESEEM spectroscopies. 13 C-carbide ENDOR of the S = 3/2 resting state (E 0 ) is remarkable, with an extremely small isotropic hyperfine coupling constant, C a = +0.86 MHz. Turnover under high CO partial pressure generates the S = 1/2 hi-CO state, with two CO molecules bound to FeMo-cofactor. This conversion surprisingly leaves the small magnitude of the 13 C carbide isotropic hyperfine-coupling constant essentially unchanged, C a = –1.30 MHz. This indicates that both the E 0 and hi-CO states exhibit an exchange-coupling scheme with nearly cancelling contributions to C a from three spin-up and three spin-down carbide-bound Fe ions. In contrast, the anisotropichyperfine coupling constant undergoes a symmetry change upon conversion of E 0 to hi-CO that may be associated with bonding and coordination changes at Fe ions. In combination with the negligible difference between CFe 6 core structures of E 0 and hi-CO, these results suggest that in CO-inhibited hi-CO the dominant role of the FeMo-cofactor carbide is to maintain the core structure, rather than to facilitate inhibitor binding through changes in Fe-carbide covalency or tretching/breaking of carbide–Fe bonds.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Cooperative asymmetric reactions combining photocatalysis and enzymatic catalysis

Living organisms rely on simultaneous reactions catalysed by mutually compatible and selective enzymes to synthesize complex natural products and other metabolites. To combine the advantages of these biological systems with the reactivity of artificial chemical catalysts, chemists have devised sequential, concurrent, and cooperative chemoenzymatic reactions that combine enzymatic and artificial catalysts. Cooperative chemoenzymatic reactions consist of interconnected processes that generate products in yields and selectivities that cannot be obtained when the two reactions are carried out sequentially with their respective substrates. However, such reactions are difficult to develop because chemical and enzymatic catalysts generally operate in different media at different temperatures and can deactivate each other. Owing to these constraints, the vast majority of cooperative chemoenzymatic processes that have been reported over the past 30 years can be divided into just two categories: chemoenzymatic dynamic kinetic resolutions of racemic alcohols and amines, and enzymatic reactions requiring the simultaneous regeneration of a cofactor. New approaches to the development of chemoenzymatic reactions are needed to enable valuable chemical transformations beyond this scope. Here in this paper we report a class of cooperative chemoenzymatic reaction that combines photocatalysts that isomerize alkenes with ene-reductases that reduce carbon–carbon double bonds to generate valuable enantioenriched products. This method enables the stereoconvergent reduction of E/Zmixtures of alkenes or reduction of the unreactive stereoisomers of alkenes in yields and enantiomeric excesses that match those obtained from the reduction of the pure, more reactive isomers. The system affords a range of enantioenriched precursors to biologically active compounds. More generally, these results show that the compatibility between photocatalysts and enzymes enables chemoenzymatic processes beyond cofactor regeneration and provides a general strategy for converting stereoselective enzymatic reactions into stereoconvergent ones.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Synthesis and electronic properties of Fe 2 TiO 5 epitaxial thin films

Here, we investigate the growth phase diagram of pseudobrookite Fe 2 TiO 5 epitaxial thin films on LaAlO 3 (001) substrates using pulsed laser deposition. Control of the oxygen partial pressure and temperature during deposition enabled selective stabilization of (100)- and (230)-oriented films. In this regime, we find an optical gap of 2.1 eV and room temperature resistivity in the range of 20–80 Ω cm, which are significantly lower than α-Fe 2 O 3 , making Fe 2 TiO 5 potentially an ideal inexpensive visible-light harvesting semiconductor. These results provide a basis to incorporate Fe 2 TiO 5 in oxide heterostructures for photocatalytic and photoelectrochemical applications.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Energetic and structural control of polyspecificity in a multidrug transporter

Multidrug efflux pumps are dynamic molecular machines that drive antibiotic resistance by harnessing ion gradients to export chemically diverse substrates. Despite their clinical importance, the molecular principles underlying multidrug promiscuity and energy efficiency remain poorly understood. Using multiparametric deep mutational scanning across eight substrates and two energy conditions, we deconvolute the contributions of substrate recognition, energetic coupling, and protein stability, providing an integrated, high-resolution view of multidrug transport. We find that substrate specificity arises from a distributed network of residues extending beyond the binding site, with mutations that reshape binding, coupling, conformational flexibility, and membrane interactions. Further, we apply a pH-based selection scheme to measure the effect of mutation on pH-dependent transport efficiency. By integrating these data, we reveal a fundamental relationship between efficiency and promiscuity: Highly efficient variants exhibit broad substrate profiles, while inefficient variants are narrower. In conclusion, these findings establish a direct link between energy coupling and polyspecificity, uncovering the biochemical logic underlying multidrug transport.

Biological Sciences↗
DOE OSTI2018

Data for Cooperative Asymmetric Reactions Combining Photocatalysis and Enzymatic Catalysis

Living organisms rely on simultaneous reactions catalysed by mutually compatible and selective enzymes to synthesize complex natural products and other metabolites. To combine the advantages of these biological systems with the reactivity of artificial chemical catalysts, chemists have devised sequential, concurrent, and cooperative chemoenzymatic reactions that combine enzymatic and artificial catalysts. Cooperative chemoenzymatic reactions consist of interconnected processes that generate products in yields and selectivities that cannot be obtained when the two reactions are carried out sequentially with their respective substrates. However, such reactions are difficult to develop because chemical and enzymatic catalysts generally operate in different media at different temperatures and can deactivate each other. Owing to these constraints, the vast majority of cooperative chemoenzymatic processes that have been reported over the past 30 years can be divided into just two categories: chemoenzymatic dynamic kinetic resolutions of racemic alcohols and amines, and enzymatic reactions requiring the simultaneous regeneration of a cofactor. New approaches to the development of chemoenzymatic reactions are needed to enable valuable chemical transformations beyond this scope. Here we report a class of cooperative chemoenzymatic reaction that combines photocatalysts that isomerize alkenes with ene-reductases that reduce carbon–carbon double bonds to generate valuable enantioenriched products. This method enables the stereoconvergent reduction of E/Z mixtures of alkenes or reduction of the unreactive stereoisomers of alkenes in yields and enantiomeric excesses that match those obtained from the reduction of the pure, more reactive isomers. The system affords a range of enantioenriched precursors to biologically active compounds. More generally, these results show that the compatibility between photocatalysts and enzymes enables chemoenzymatic processes beyond cofactor regeneration and provides a general strategy for converting stereoselective enzymatic reactions into stereoconvergent ones.

Catalysis↗
DOE OSTI2024

High-Efficiency and Low-Carbon Energy Storage and Power Generation System for Electric Aviation

This report summarizes the work performed by University of California San Diego (UCSD) – Honeywell Aerospace (Honeywell) team for the U.S. Department of Energy/Advanced Research Projects Agency-Energy (DOE/ARPA-E) under Phase 1 (April 2021 – October 2023) project, Cooperative Agreement DE-AR0001347 entitled “High-Efficiency and Low-Carbon Energy Storage and Power Generation System for Electric Aviation”. The main objective of this project is to develop and demonstrate an energy storage and power generation (ESPG) system operating on bio liquid natural gas (LNG) for electric aviation applications. The ESPG system concept in this project is a fuel cell, battery, and gas turbine hybrid system that incorporates an innovative solid oxide fuel cell (SOFC) technology. This SOFC technology has two main novel elements: (i) a lightweight and compact stack architecture that consists of cells and cell modules in electrical parallel and series connections (the module design) and (ii) exceptionally high performance, direct methane thin-film cells on porous substrate made by sputtering deposition process. This fuel cell has the specific power and volumetric power density suitable for electric aviation applications. Based on the current status of the SOFC technology, the Phase 1 work focused on the following activities: (i) ESPG System Modeling – to design and optimize an aircraft SOFC-based ESPG system concept that met the performance, weight and cost targets; (ii) Cell Material Development and Scaleup – to demonstrate scalability of the sputtering process for manufacture of thin-film SOFC cells of practical sizes, confirm the exceptional performance of sputtered cells, improve cell stability and durability for operation with hydrogen and methane fuel, and develop a suitable electrically conducting porous substrate to replace the current non-conducting ceramic substrate; (iii) Stack Development – to design and manufacture stack components for the stack architecture, evaluate and select a suitable sealant, and build and operate multi-cell stacks to demonstrate stack operation, and (iv) Technology to Market – to develop business models and commercialization plans, conduct various market and technology analysis and estimate SOFC and ESPG system costs.

25 ENERGY STORAGE↗
NASA NTRS1982

Liquid encapsulated Czochralski growth of low dislocation GaAs

The availability of high-quality, large-diameter GaAs substrates is key to the successful development and production of high-speed GaAs devices and high-efficiency GaAs solar cells. The liquid encapsulated Czochralski (LEC) technique has provided a means for producing large-diameter GaAs. Progress in improving the LEC growth process which has resulted in 3-inch GaAs crystals with exceptionally low dislocation densities and reduced propensity for twinning is reported. Undoped, semi-insulating GaAs ingots were grown in a Melbourn high-pressure LEC system. The effects of seed perfection, seed necking, cone angle, melt stoichiometry, ambient pressure, thickness of the B2O3 encapsulating layer, and diameter control on the dislocation density were investigated. The material was characterized by preferential etching and X-ray topography. It is shown that 3-inch diameter substrates can be produced with dislocation densities as low as 6000 per sq cm through proper selection and control of growth parameters. Also, the incidence of twinning can be reduced significantly by growing from slightly As-rich melts.

Kirkpatrick, C. G.↗
NASA NTRS1986

Adhesive joint evaluation by ultrasonic interface and lamb waves

Some results on the application of interface and Lamb waves for the study of curing of thin adhesive layers were summarized. In the case of thick substrates (thickness much more than the wave length) the interface waves can be used. In this case the experimental data can be inverted and the shear modulus of the adhesive film may be explicitly found based on the measured interface wave velocity. It is shown that interface waves can be used for the study of curing of structural adhesives as a function of different temperatures and other experimental conditions. The kinetics of curing was studied. In the case of thin substrates the wave phenomena are much more complicated. It is shown that for successful measurements proper selection of experimental conditions is very important. This can be done based on theoretical estimations. For correctly selected experimental conditions the Lamb waves may be a sensitive probe of adhesive bond quality and may be used or cure monitoring.

Rokhlin, S. I.↗
NASA NTRS1999

Immunoassay readout method using extrinsic Raman labels adsorbed on immunogold colloids

An immunoassay readout method based on surface-enhanced Raman scattering (SERS) is described. The method exploits the SERS-derived signal from reporter molecules that are coimmobilized with biospecific species on gold colloids. This concept is demonstrated in a dualanalyte sandwich assay, in which two different antibodies covalently bound to a solid substrate specifically capture two different antigens from an aqueous sample. The captured antigens in turn bind selectively to their corresponding detection antibodies. The detection antibodies are conjugated with gold colloids that are labeled with different Raman reporter molecules, which serve as extrinsic labels for each type of antibody. The presence of a specific antigen is established by the characteristic SERS spectrum of the reporter molecule. A near-infrared diode laser was used to excite efficiently the SERS signal while minimizing fluorescence interference. We show that, by using different labels with little spectral overlap, two different antigenic species can be detected simultaneously. The potential of this concept to function as a readout strategy for multiple analytes is briefly discussed.

NASA Program Advanced Human Support Technology↗
DOE OSTI2016

Cristallini Material Review and Selection

The creation of a handheld unit to utilize the Cristallini method of uranium hexafluoride sampling requires the identification and qualification of suitable substrate materials. These materials will need to quickly and completely react with the process gas, resist vapor locking under vacuum, while being relatively inexpensive and homogeneous. Two forms of powdered alumina have been chosen for a head-to-head comparison during upcoming uranium hexafluoride tests. Both materials have shown ideal uptake characteristics during tungsten hexafluoride tests with a high loading capacity and no measureable breakthrough. They have also been shown to work well at vacuums below 10 Torr, are commercially available and inexpensive. In addition, two possible hydrogen fluoride trapping materials, sodium fluoride and saturated calcium carbonate, have been identified for further testing.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS1981

Unsteady environments and responses of the shuttle combined loads orbiter test

Both separate and combined wind tunnel and vibration shaker tests were conducted on two structural panels representative of the Shuttle orbiter in the NASA LaRC 8-foot transonic pressure tunnel (TPT) to determine the effects of combined loads on the thermal protection system (TPS). The primary objective of this test was to provide a combined full-scale load environment and realistic time history of the dynamic pressures, Mach numbers (through transonic), and dynamic structural responses of these panels. The panels were selected from orbiter locations where interactive load sources such as aerodynamic shock waves, turbulent boundary layers, strut-induced vorticity, and substrate deformation combined to provide high bonding loads between the TPS and the orbiter structure. The test panels for this program were highly instrumented with static and dynamic pressure gages, accelerometers, deflectometers, strain gages, Schileren and high-speed photography, and special instrumentation necessary to determine TPS/structure interface loads and tile motions. Two test specimens of each orbiter panel were utilized. Both were high-fidelity representations of the selected orbiter location. The first panel (calibration panel) for each test was utilized to calibrate the tunnel and shaker system as well as provide a data-gathering source for applied static and dynamic loads. The second panel (test panel) for each test was subjected to flight time exposures only so that TPS characteristics as a function of flight mission exposure could be determined. These tests were the last in a series that was suce6ssfully completed and necessary to certify the TPS prior to the first launching of the Shuttle.

P. H. Schuetz↗
NASA NTRS2004

Selection of Optical Cavity Surface Coatings for 1micron Laser Based Missions

The particulate surface cleanliness level on several coatings for aluminum and beryllium substrates were examined for use in the optical cavities of high pulse energy Nd:YAG Q-switched, diode-pumped lasers for space flight applications. Because of the high intensity of the lasers, any contaminants in the laser beam path could damage optical coatings and limit the instrument mission objectives at the operating wavelength of 1 micron (micrometer). Our goal was to achieve an EST-STD-CC1246D Level 100 particulate distribution or better to ensure particulate redistribution during launch would not adversely affect the performance objectives. Tapelifts were performed to quantify the amount of particles using in-house developed procedures. The primary candidate coatings included chromate conversion coating aluminum (Al), uncoated Al electroless Nickel (Ni) on Al, Ni-gold (Au) on Al, anodized Al, and gold (Au)/Ni on Beryllium (Be). The results indicate that there were advantages in Ni and Au coating applications for the two major substrates, Al and Be, when considering applications that need to meet launch environments.

Hedgeland, Randy J.↗
DOE OSTI2017

Selective Targeting by a Mechanism-Based Inactivator against Pyridoxal 5'-Phosphate-Dependent Enzymes: Mechanisms of Inactivation and Alternative Turnover

Potent mechanism-based inactivators can be rationally designed against pyridoxal 5'-phosphate (PLP)-dependent drug targets, such as ornithine aminotransferase (OAT) or γ-aminobutyric acid aminotransferase (GABA-AT). An important challenge, however, is the lack of selectivity toward other PLP-dependent, off-target enzymes, because of similarities in mechanisms of all PLP-dependent aminotransferase reactions. On the basis of complex crystal structures, we investigate the inactivation mechanism of OAT, a hepatocellular carcinoma target, by (1R,3S,4S)-3-amino-4-fluorocyclopentane-1-carboxylic acid (FCP), a known inactivator of GABA-AT. A crystal structure of OAT and FCP showed the formation of a ternary adduct. This adduct can be rationalized as occurring via an enamine mechanism of inactivation, similar to that reported for GABA-AT. Interestingly, however, the crystal structure of an off-target, PLP-dependent enzyme, aspartate aminotransferase (Asp-AT), in complex with FCP, along with the results of attempted inhibition assays, suggests that FCP is not an inactivator of Asp-AT, but rather an alternate substrate. Turnover of FCP by Asp-AT is also supported by high-resolution mass spectrometry. Amid existing difficulties in achieving selectivity of inactivation among a large number of PLP-dependent enzymes, the obtained results provide evidence that a desirable selectivity could be achieved, taking advantage of subtle structural and mechanistic differences between a drug-target enzyme and an off-target enzyme, despite their largely similar substrate binding sites and catalytic mechanisms.

59 BASIC BIOLOGICAL SCIENCES↗